This invention relates to an end wall for a container and more particularly but not exclusively to an end wall of a can body and a method for fixing the end wall to the can body by means of a double seam.
U.S. Pat. No. 4,093,102 (KRASKA) describes can ends comprising a peripheral cover hook, a chuck wall dependent from the interior of the cover hook, an outwardly concave annular reinforcing bead extending radially inwards from the chuck wall and a central panel joined to an inner wall of the reinforcing bead by an annular outwardly convex bead. This can end is said to contain an internal pressure of 90 psi by virtue of the inclination or slope of the chuck wall, bead outer wall and bead inner wall to a line perpendicular to the centre panel. The chuck wall slope D° is between 14° and 16°, the outer wall slope E is less than 4° and the inner wall slope C° is between 10 and 16° leading into the outwardly convex bead. We have discovered that improvements in metal usage can be made by increasing the slope of the chuck wall and limiting the width of the anti peaking bead.
U.S. Pat. No. 4,217,843 (KRASKA) describes an alternative design of can end in which the countersink has inner and outer flat walls, and a bottom radius which is less than three times the metal thickness. The can end has a chuck wall extending at an angle of approximately 24° to the vertical. Conversely, the specification of our U.S. Pat. No. 5,046,637 describes a can end in which the chuck wall extends at an angle of between 12° and 20° to the vertical.
The detailed description of our U.S. Pat. No. 4,571,978 describes a method of making a can end suitable for closing a can body containing a beverage such as beer or soft drinks. This can end comprises a peripheral flange or cover hook, a chuck wall dependant from the interior of the cover hook, an outwardly concave reinforcing bead extending radially inwards from the chuck wall from a thickened junction of the chuck wall with the bead, and a central panel supported by an inner portion of the reinforcing bead. Such can ends are usually formed from a prelacquered aluminum alloy such as an aluminum magnesium manganese alloy such as alloy 5182.
The specification of our U.S. Pat. No. 5,582,319 describes a can end suitable for a beverage can and formed from a laminate of aluminum/manganese alloy coated with a film of semi crystalline thermoplastic polyester. This polyester/aluminum alloy laminate permitted manufacture of a can end with a narrow, and therefore strong reinforcing bead in the cheaper aluminum manganese alloy.
These known can ends are held during double seaming by an annular flange of chuck, the flange being of a width and height to enter the anti-peaking bead. There is a risk of scuffing if this narrow annulus slips. Furthermore a narrow annular flange of the chuck is susceptible to damage.
Continuing development of a can end using less metal, whilst still permitting stacking of a filled can upon the end of another, this invention provides a can end comprising a peripheral cover hook, a chuck wall dependant from the interior of the chuck wall, an outwardly concave annular reinforcing bead extending radially inwards from the chuck wall, and a central panel supported by an inner portion of the reinforcing bead, characterized in that, the chuck wall is inclined to an axis perpendicular to the exterior of the central panel at an angle between 30° and 60°, and the concave bead narrower than 1.5 mm (0.060″). Preferably, the angle of the chuck wall to the perpendicular is between 40° and 45°.
In a preferred embodiment of the can end an outer wall of the reinforcing bead is inclined to a line perpendicular to the central panel at an angle between −15° to +15° and the height of the outer wall is up to 2.5 mm.
In one embodiment the reinforcing bead has an inner portion parallel to an outer portion joined by said concave radius.
The ratio of the diameter of the central panel to the diameter of the peripheral curl is preferably 80% or less.
The can end may be made of a laminate of thermoplastic polymer film and a sheet aluminum alloy such as a laminate of a polyethylene terephthalate film on an aluminum-manganese alloy sheet or ferrous metal typically less than 0.010 (0.25 mm) thick for beverage packaging. A lining compound may be placed in the peripheral cover hook.
In a second aspect this invention provides a method of forming a double seam between a can body and a can end according to any preceding claim, said method comprising the steps of:
placing the curl of the can end on a flange of a can body supported on a base plate, locating a chuck within the chuck wall of the can end to centre the can end on the can body flange, said chuck having a frustoconical drive surface of substantially equal slope to that of the chuck wall of the can end and a cylindrical surface portion extending away from the drive surface within the chuck wall, causing relative motion as between the assembly of can end and can body and a first operation seaming roll to form a first operation seam, and thereafter causing relative motion as between the first operation seam and a second operation roll to complete a double seam, during these seaming operations the chuck wall becoming bent to contact the cylindrical portion of the chuck.